Mass

Size

Discovery Methods

NGC 3377

NGC 3377 is an elliptical galaxy, and it appears as a well-defined oval, instead of a near-circle or a thin cigar-shape. It is a member of a group of more than a dozen galaxies that cluster together in the constellation Leo.

This galaxy has been closely studied with Hubble Space Telescope as part of an extensive survey undertaken by an international team of astronomers. The research team used HST to observe 27 galaxies, looking for evidence of massive black holes. Their conclusion: not only do most galaxies appear to have these black holes at their centers, but the mass of the black hole is closely connected to the mass of the whole galaxy. This relationship is a vital clue for understanding how the black holes are formed.

In addition to the observations from HST, NGC 3377 has been observed with two ground-based telescopes using a novel type of spectrograph instrument. Most telescopes are equipped to collect the light from a star or a small section of a galaxy, and

split the light into its individual wavelengths to determine characteristics like speed, temperature, or composition. These instruments, however, cannot study the light from an entire galaxy because it appears too large; the light from all the stars and gas clouds smears together, so astronomers cannot make precise measurements of individual regions of the galaxy.

The two new spectrographs, named OASIS and SAURON, use a clever optical trick to get around this problem. The image of the target galaxy is focused upon an array of tiny lenses, like the eye of a fly, which breaks the image of a galaxy into hundreds of separate points of light. Each light spot can then be spread out into a spectrum without the adjacent spectra crashing into each other. It requires sophisticated computer software to extract and analyze each of the hundreds of individual spectra, but the end result is a map of the star velocities in each separate region of the galaxy -- exactly what astronomers need to trace the gravitational pull of the unseen black hole and calculate its mass.